Galatian War

The Galatian War was a military conflict fought in the 20s BC between the Roman Empire and its rebellious vassal, Galatia. Emperor Augustus and the Roman Senate decided to send aid to their client kingdom of Cappadocia when King Deiotarus II of Galatia invaded Cappadocian lands in a bid to unite much of Asia Minor under his rule. The Galatians made good progress, conquering a large stretch of territory in the center and south of the peninsula. However, the Romans were able to launch a counterattack and retake the lost territories, in addition to killing Deiotarus in battle. The result of the war was the subjugation of Galatia as a province under direct Roman rule.

Background
In the aftermath of Julius Caesar's defeat of the once-powerful Anatolian kingdom of Pontus at Zela in 47 BC, all of Asia Minor fell under the control of the Roman Republic. Around a third of the peninsula was ruled through client kings, including those of Pontus, Galatia, and Cappadocia. After the foundation of the Roman Empire by Augustus in 27 BC, all of Rome's client rulers became hostile towards the new Roman emperor, but Augustus began to build a positive reputation by assisting them whenever they sent out calls for help in defensive wars. That same year, Augustus conquered the lands of the Scordisci in response to a plea from the Odrysian Kingdom of Thrace, and he prevented a threat to his Iberian vassals by conquering the Cantabri. However, he decided against siding with the weak Belgae against his other vassal, Gaul, as Roman-ruled Gaul was under-defended, and he could not afford another war on the western frontier.

In 26 BC, however, a more pressing issue arose when the ambitious Roman client ruler of Galatia, Deiotarus II, decided to invade the lands of Cappadocia, another Roman client state. Cappadocia sent envoys to Rome to ask for assistance from Emperor Augustus, who was interested in absorbing more of his client states into his empire, which he could only do through force. He decided to send Titus Statilius Taurus' Legio III Asiana to intervene in the war on the side of Cappadocia, giving him a pretext to conquer Galatia.

Galatian offensive
Shortly after Rome accepted Cappadocia's request for intervention in the war, King Deiotarus had the excuse he needed to conquer some of Rome's undefended cities in Anatolia. His 1,640-strong army campaigned through central Anatolia, first conquering Iconium and then advancing south to capture the port of Side from its garrison army and fleet. Galatia briefly owned almost a fifth of all of Anatolia, emerging as a major threat to Roman rule.

Roman counterattack
In 25 BC, the Romans struck back. Legio III Asiana (with a strength of 2,400 troops), hastily bolstered by locally-recruited mercenaries, conquered the Galatian capital of Ancyra after a siege which involved light casualties. As the winter of 25 BC changed into spring - campaigning season - Deiotarus offered the Romans 440 talents if they would accept a peace treaty, which would leave Galatia in charge of its new conquests, but not its original capital. The Romans refused to let the Galatians keep their conquests, and they immediately rejected these terms. In the spring of 25 BC, the Romans laid siege to Iconium, where Deiotarus had taken his army after his victory at Side, hoping to defend his new conquests.